The invention relates to ethylene-propylene elastomer-based insulating (or semi-conductive) electrical tape containing thermally conductive non-reinforcing filler.
Insulating tapes are required to replace electrical insulation which has been stripped from a conductor for any of a variety of reasons. For example, where two conductors are joined together to make a splice, such insulating tape is required to provide an insulating sheath over the joined ends of the splice. The insulating tape may be of the so called "self-fusing" type wherein the tape is in the form of a strip of elastomeric material which, when wrapped convolutely upon itself, will fuse together practically free of voids so that the layers become indistinguishable and paths for moisture to enter are excluded. Such self-fusing tapes are described in U.S. Pat. Nos. 3,470,127 and 3,684,644. Or, the tape may be in the form of an elastomeric strip which is coated with a pressure-sensitive adhesive material such as described in U.S. Pat. Nos. 3,876,454 and 3,684,644.
While the products described in these patents have been extremely commercially successful and found great acceptance throughout the industry, these and other similar products have been found to be deficient in situations involving electrical conductors which develop relatively high temperatures because of being subjected to high current densities.
Under such circumstances, the conductor and/or connector in the area of a splice or termination where such tape is typically required may be raised to a temperature which can cause a physical change or breakdown in the composition of an insulating tape and/or cable insulation. Such breakdowns are characterized by an increase of the temperature of the conductor and/or connector which typically causes increased resistance with rapid heat build up until the polymer material forming the tape is degraded. In the case of a splice, the temperature of the splice connector may exceed the maximum recommended operating temperature which can cause an increase in the contact resistance of the connector, resulting in further temperature build up. Such degradation of the insulating tape can cause mechanical and/or electrical failure.
Present prior art insulating tapes employed to replace insulation when a splice or termination is made are generally rated to withstand continuous operation at temperatures as high as 90.degree. C and to withstand 500 hours at an overload temperature of 130.degree. C. In the past, demands upon electrical power have been relatively moderate so that electrical conductors, e.g., cables and/or wires, have not generally been operated at their maximum capacity. Present day and future power demands, however, are much higher and, if they are not presently, many electrical power conductors will be operated at current densities which will cause heating to temperatures near or above the maximum rating for cables, connectors, insulating materials, and other equipment normally employed in electrical power distribution.